1. Field of the Invention
The present invention relates to an organic EL Device and a method for manufacturing the same.
2. Description of Related Art
FIG. 1 is a cross-sectional view illustrating a conventional organic EL device. As shown in FIG. 1, the organic EL device includes a first electrode or anode electrode 13 formed on a substrate 11 and a second electrode or cathode electrode 15 with an EL light-emitting layer 17 interposed therebetween.
A method for manufacturing such an organic EL device is as follows. First, an indium-tin oxide (ITO) film is formed all over a front surface of a glass substrate in a vacuum atmosphere. Then, the ITO film is formed into a stripe-like shape by etching, forming a plurality of transparent electrodes or first electrodes 13 arranged side by side but spaced apart from each other at predetermined intervals. Then, the EL light-emitting layer 17 is formed on the first electrode 13. The EL light-emitting layer 17 includes a hole transport layer, a luminescent layer, and an electron transport layer, laminated in sequence and sandwiched between an anode and a cathode.
The hole transport layer, which is made of a hole transport material such as a triphenylamine derivative (TPD) or the like, is formed on the transparent electrodes by vacuum deposition. Subsequently, a layer made of an electron transport material such as an aluminum quinolinol complex (Alq3) acting as a luminous material is laminated on the hole transport layer, resulting in a luminous material layer being formed by vacuum deposition. Then, material such as Al, Li, Ag, Mg, In is deposited in a stripe-like manner on the luminous material layer so as to extend in a direction perpendicular to a pattern of the transparent electrodes, to thereby provide a plurality of rear electrodes or second electrodes 15. In such a construction, portions of the luminous material layer positioned at intersections between the transparent electrodes and the rear electrodes define luminous sections, in forming a dot matrix. The organic EL device thus constructed flows current to the luminous sections positioned on the intersections between the transparent electrodes acting as anodes and the rear electrodes acting as cathodes, illuminating the luminous sections.
However, the organic EL device having such a configuration has a problem of low contrast, because ambient light is reflected from the second electrode 15 made of a metal.
In order to overcome the problem described above, as shown in FIG. 2, a retardation film 19 and a polarizer 18 are sequentially arranged on a lower surface of the substrate 11, which. At this point, the retardation film is made of xcex/4 plate. The polarizer 18 and the retardation film 19 causes a phase difference in ambient light reflected from the cathode electrode 15, leading to a destructive interference, whereupon ambient light is blocked. In other words, the first quarter-wave plate and the polarizer cooperatively work as a circularly polarizer plate that can absorb light reflected from the cathode electrode, thus reducing reflection.
However, the polarizer 18 and the retardation film 19 lowers a light transmittance to be less than about 50%. As a result, a brightness of the organic EL device is as lowered as about 50%.
To overcome the problems described above, preferred embodiments of the present invention provide an organic EL device having a high contrast ratio and a high brightness.
In order to achieve the above object, the preferred embodiments of the present invention provide an organic EL device. A transparent substrate has a display region and a non-display region. The display region has pixel regions. First electrodes are formed on the display region of the substrate and spaced apart from each other. EL light-emitting layers are formed on the portions of the first electrode corresponding to the pixel region. Second electrodes are formed over the display region and have a light absorbing layer interposed therein.
Further, an interlayer insulator is formed over a portion of the display region except for portions of the first electrode corresponding to the pixel region, and overhanging shaped partition walls are formed on the interlayer insulator in a perpendicular direction to the first electrodes.
The preferred embodiment of the present invention provides a method for manufacturing an organic EL device. The method includes a) providing a transparent substrate having a display region and a non-display region, the display region having a pixel region; b) forming first electrodes formed on the substrate, the first electrode spaced apart from each other; c) forming EL light-emitting layers on the portions of the first electrode corresponding to the pixel region; and d) forming second electrodes over the display region, the second electrode having a light absorbing layer interposed therein.
The method further includes, after the step of (b), forming interlayer insulator, the interlayer insulator over a portion of the display region except for portions of the first electrode corresponding to the pixel region; forming partition walls on the interlayer insulator in a perpendicular direction to the first electrodes.
The second electrode includes first and second layers with the light absorbing layer interposed therebetween. The first layer is adjacent to the EL light-emitting layer ID and has a thin thickness sufficiently to transmit part of ambient light. The first layer of the second electrode is less than about 100 xc3x85 thicks. The second layer is thicker than the first layer. The black layer of the second electrode is disposed on a location corresponding to the pixel region. The black layer is made of a material absorbing ambient light. The black layer is made of one of carbon, an inorganic material, and an organic material. The organic EL device further includes cathode leads formed on the non-display region of the substrate and electrically connected with the second electrode. The interlayer insulator includes a contact hole, and the cathode leads are electrically connected to the second electrode through the contact hole. The first electrode is made of indium tin oxide (ITO). The second electrode is made of one of Al, Li, Mg, Ag, Ca, Ba, and so on.
Since ambient light is partially transmitted through the thin first layer of second electrode and is subsequently absorbed by the black layer, the contrast ratio increases, leading to higher brightness.